ADD file via upload

mpi_trap3.c

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+/* File:     mpi_trap3.c
+ * Purpose:  Use MPI to implement a parallel version of the trapezoidal 
+ *           rule.  This version uses collective communications to 
+ *           distribute the input data and compute the global sum.
+ *
+ * Input:    The endpoints of the interval of integration and the number
+ *           of trapezoids
+ * Output:   Estimate of the integral from a to b of f(x)
+ *           using the trapezoidal rule and n trapezoids.
+ *
+ * Compile:  mpicc -g -Wall -o mpi_trap2 mpi_trap2.c
+ * Run:      mpiexec -n <number of processes> ./mpi_trap2
+ *
+ * Algorithm:
+ *    1.  Each process calculates "its" interval of
+ *        integration.
+ *    2.  Each process estimates the integral of f(x)
+ *        over its interval using the trapezoidal rule.
+ *    3a. Each process != 0 sends its integral to 0.
+ *    3b. Process 0 sums the calculations received from
+ *        the individual processes and prints the result.
+ *
+ * Notes:  
+ *    1. f(x) is all hardwired.
+ *    2. The number of trapezoids should be evenly divisible by
+ *       the number of processes.
+ *
+ * IPP2:  Section 3.4.2 (pp. 110 and ff.)
+ */
+#include <stdio.h>
+
+/* We'll be using MPI routines, definitions, etc. */
+#include <mpi.h>
+
+/* Get the input values */
+void Get_input(int my_rank, int comm_sz, double* a_p, double* b_p,
+      int* n_p);
+
+/* Calculate local integral  */
+double Trap(double left_endpt, double right_endpt, int trap_count, 
+   double base_len);    
+
+/* Function we're integrating */
+double f(double x); 
+
+int main(void) {
+   int my_rank, comm_sz, n, local_n;   
+   double a, b, h, local_a, local_b;
+   double local_int, total_int;
+
+   /* Let the system do what it needs to start up MPI */
+   MPI_Init(NULL, NULL);
+
+   /* Get my process rank */
+   MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
+
+   /* Find out how many processes are being used */
+   MPI_Comm_size(MPI_COMM_WORLD, &comm_sz);
+
+   Get_input(my_rank, comm_sz, &a, &b, &n);
+
+   h = (b-a)/n;          /* h is the same for all processes */
+   local_n = n/comm_sz;  /* So is the number of trapezoids  */
+
+   /* Length of each process' interval of
+    * integration = local_n*h.  So my interval
+    * starts at: */
+   local_a = a + my_rank*local_n*h;
+   local_b = local_a + local_n*h;
+   local_int = Trap(local_a, local_b, local_n, h);
+
+   /* Add up the integrals calculated by each process */
+   /* 第2处代码补全开始 */
+   
+   /* 第2处代码补全结束 */
+
+   /* Print the result */
+   if (my_rank == 0) {
+      printf("%.3f\n", total_int);
+   }
+
+   /* Shut down MPI */
+   MPI_Finalize();
+
+   return 0;
+} /*  main  */
+
+/*------------------------------------------------------------------
+ * Function:     Get_input
+ * Purpose:      Get the user input:  the left and right endpoints
+ *               and the number of trapezoids
+ * Input args:   my_rank:  process rank in MPI_COMM_WORLD
+ *               comm_sz:  number of processes in MPI_COMM_WORLD
+ * Output args:  a_p:  pointer to left endpoint               
+ *               b_p:  pointer to right endpoint               
+ *               n_p:  pointer to number of trapezoids
+ */
+void Get_input(int my_rank, int comm_sz, double* a_p, double* b_p,
+      int* n_p) {
+
+   if (my_rank == 0) {
+      scanf("%lf %lf %d", a_p, b_p, n_p);
+   } 
+   /* 第1处代码补全开始 */
+   /* 使用MPI_Bcast将a_p、b_p、n_p发送给其他进程 */
+   
+   /* 第1处代码补全结束 */
+}  /* Get_input */
+
+/*------------------------------------------------------------------
+ * Function:     Trap
+ * Purpose:      Serial function for estimating a definite integral 
+ *               using the trapezoidal rule
+ * Input args:   left_endpt
+ *               right_endpt
+ *               trap_count 
+ *               base_len
+ * Return val:   Trapezoidal rule estimate of integral from
+ *               left_endpt to right_endpt using trap_count
+ *               trapezoids
+ */
+double Trap(
+      double left_endpt  /* in */, 
+      double right_endpt /* in */, 
+      int    trap_count  /* in */, 
+      double base_len    /* in */) {
+   double estimate, x; 
+   int i;
+
+   estimate = (f(left_endpt) + f(right_endpt))/2.0;
+   for (i = 1; i <= trap_count-1; i++) {
+      x = left_endpt + i*base_len;
+      estimate += f(x);
+   }
+   estimate = estimate*base_len;
+
+   return estimate;
+} /*  Trap  */
+
+
+/*------------------------------------------------------------------
+ * Function:    f
+ * Purpose:     Compute value of function to be integrated
+ * Input args:  x
+ */
+double f(double x) {
+   return x*x;
+} /* f */